Today marks an entire week of using Haiku as my primary operating system. This
is my first PC to get the most out of any BeOS related operating system to date.
My old 200MHz Toshiba ran R5 PE just fine but without any networking. My
eMachine ran Zeta just fine, but once again, there were networking issues (and
Zeta was pronounced dead around this time). In the age of the Internet, this
pretty much forced me away from BeOS and its decendants until now.

Linux in 4 years will still be using the "bazaar" model for most of it's userland. So it will still be an unpolished incoherent OS with little attention to detail. That has no hope of getting ever fixed.
Also at the current rate, in 4 years Linux will require a 50 core CPU with 50 Gigs of RAM to be able to run decently as a desktop. So that's why even waiting 20 years for Haiku is preferable.

It isn't the Linux kernel that is the problem. It's the "Linux" userspace.

Developers aren't taking any care with RAM requirements. They hardly ever test with serious amounts of data (Nobody has 500,000 emails in their IMAP. That would be crazy!). They don't stop to think about performance issues with 4,200 RPM laptop drives (We will have our file picker seek all over the disk to read an icon for each file in the directory! Oh, we never tested that with 10,000 files...) And they never examine the disk seek behavior of their application on a cold cache start (Oh, Firefox can read every little xul and css and jar file one at a time to start up...Windows Vista will preload all that for us!)